This invention relates to tissue supporting devices in general and most particularly to vascular stents for placement in blood vessels. A primary feature of the devices of this invention is that they are expandable within the body.
In the past, such devices have been provided for implantation within body passageways. These devices have been characterized by the ability to be enlarged radially, often having been introduced into the desired position in the body as by percutaneous techniques or surgical techniques.
These devices are either expanded mechanically, such as by expansion of a balloon positioned inside the device, or are capable of releasing stored energy to self-expand themselves within the body.
The materials which have been used to make up these devices have included ordinary metals, shape memory alloys, various plastics, both biodegradable and not, and the like.
This invention is concerned with the use of these materials in a new multiple component arrangement which allows for initial self-expansion and subsequent deformation to a final enlarged diameter in the body.
Balloon expandable stents do not always expand uniformly around their circumference. As a result, healing may not take place in a consistent manner. If the stent is coated or covered, non-uniform expansion may tear the covering or coating. Additionally, long stents of this type may require long balloons which can be difficult to handle, difficult to size, and may not offer ideal performance in tortuous passages in blood vessels and the like.
Thus, when addressing such issues, self-expandable stents have been thought to be generally more desirable. Unfortunately, one cannot control the degree of expansion and hence the degree of embedment in the vessel wall. It has been determined that a stent must be embedded to some degree to be clinically satisfactory.
The stents of the present invention provide the best features of both of these types of stents without their drawbacks.
The tissue supporting devices of this invention are generally cylindrical or tubular in overall shape and of such a configuration as to allow radial expansion for enlargement. They are often referred to herein in the general sense as xe2x80x9cstentsxe2x80x9d. Furthermore, the devices are comprised of at least one component, element, constituent or portion which exhibits a tendency to self-expand the device to an expanded size and at least one other component, element, constituent or portion which is deformable so as to allow an external force, such as a balloon positioned within the body of the device, to further expand it to a final, larger desired expanded size. The terms xe2x80x9ccomponentxe2x80x9d, xe2x80x9celementxe2x80x9d, xe2x80x9cconstituentxe2x80x9d and xe2x80x9cportionxe2x80x9d are often referred to herein collectively as xe2x80x9cportionxe2x80x9d.
Preferably, the devices of the invention are made of metal and most preferably of shape memory alloys.
In one embodiment, a first portion is a resilient spring-like metal for self-expansion and a second portion is a deformable metal for final sizing. In a more preferred shape memory embodiment, a first portion is a self-expanding austenitic one and a second is a martensitic one capable of deformation. In the case of shape memory embodiments the xe2x80x9cportionsxe2x80x9d may be discrete or merely different phases of an alloy.
The most preferred embodiment of the invention is a stent, preferably of shape memory alloy. The most preferred shape memory alloy is Nixe2x80x94Ti, although any of the other known shape memory alloys may be used as well. Such other alloys include: Auxe2x80x94Cd, Cuxe2x80x94Zn, Inxe2x80x94Ti, Cuxe2x80x94Znxe2x80x94Al, Tixe2x80x94Nb, Auxe2x80x94Cuxe2x80x94Zn, Cuxe2x80x94Znxe2x80x94Sn, Cuxe2x80x94Znxe2x80x94Si, Cuxe2x80x94Alxe2x80x94Ni, Agxe2x80x94Cd, Cuxe2x80x94Sn, Cuxe2x80x94Znxe2x80x94Ga, Nixe2x80x94Al, Fexe2x80x94Pt, Uxe2x80x94Nb, Tixe2x80x94Pdxe2x80x94Ni, Fexe2x80x94Mnxe2x80x94Si, and the like. These alloys may also be doped with small amounts of other elements for various property modifications as may be desired and as is known in the art.
The invention will be specifically described hereinbelow with reference to stents, a preferred embodiment of the invention although it is broadly applicable to tissue support devices in general.